#1339 regression. Referenced variants boards do not have variant folder

This was caused by asking the platformPath instead of the latest
installed platformVersion Path

Author: jantje

io.sloeber.core/src/io/sloeber/core/api/BoardsManager.java

@@ -738,7 +738,11 @@ public static IPath getPlatformInstallPath(String vendor, String architecture) {
 
         ArduinoPlatform platform = getPlatform(vendor, architecture);
         if (platform != null) {
-            return new org.eclipse.core.runtime.Path(platform.getInstallPath().toString());
+            ArduinoPlatformVersion latestInstall = platform.getNewestInstalled();
+            if (latestInstall == null) {
+                return null;
+            }
+            return latestInstall.getInstallPath();
         }
         return null;
     }